There has heretofore been known a drive apparatus of a vehicle including a differential mechanism through which an output of a drive power source, such as an engine or the like, is distributed to a first electric motor and an output member, and a second electric motor disposed between the output member and drive wheels. Such drive apparatus for a hybrid vehicle is disclosed for example in JP 2003-127679A, JP 9-170533A, JP 2000-316205A and JP 2003-161181A. It includes a differential mechanism being comprised of a planetary gear unit i.e., gear set and performing as the differential action for mechanically transmitting a major part of power outputted from the engine to drive wheels. A remaining part of power from the engine is electrically transmitted from the first electric motor to the second electric motor using an electrical path. Thus, the drive apparatus operates a transmission of which shifting ratio i.e., speed ratio is electrically changed, for example as an electrically controlled continuously variable automatic transmission. The drive apparatus is controlled by the control apparatus so that the vehicle runs i.e., is driven with the optimum operation state of the engine, thus improving fuel consumption, i.e., mileage.
In general, the continuously-variable transmission has heretofore been known as a device for improving fuel consumption of a vehicle. A gear type power transmitting device such as a step-variable automatic transmission has heretofore been known as a device having high transmitting efficiency. However, no power transmitting mechanism having such combined advantages has been put into practical use yet. For instance, the hybrid vehicle drive apparatus, disclosed in the above Patent Publications, includes the electrical path through which electric energy is transmitted from the first electric motor to the second electric motor, that is, a transmitting path through which a part of the vehicle drive force is transmitted in the form of electric energy. This inevitably causes the first electric motor to be made large-size with an increase in an output of the engine. Also, the second electric motor, driven with electric energy output from the first electric motor, is caused to increase in size. Thus, an issue arises with the occurrence of an increase in size of the drive apparatus.
In addition, there was a problem that the second electric motor driven by electric energy outputted from the first electric motor need to be made large-size, which in turn makes the drive apparatus large-size. Alternately, the part of the engine output is transmitted to the driving wheel after converted to the electric energy once, which may worsen the mileage depending on the vehicle running condition such as the high speed running i.e., driving. Similar problem may occur when the above power distributing mechanism is used as the continuously variable machine called as the electrically controlled CVT in which the shifting ratio is electrically changed.
Meanwhile, with the hybrid vehicle disclosed in JP 2003-127679A, the first electric motor is turned on to increase the output rotating speed, that is, the first electric motor is rendered operative to function as a starter, thereby drivably rotating (cranking up) the engine. With the engine speed raised at a level higher than a given engine speed, that is, for instance, a level higher than the engine speed at which the engine autonomously rotates, fuel is injected to the engine for ignition, thereby starting up the engine.
Further, in general, the vehicle encounters vibration and noise in various patterns. For instance, fluctuation occurs in the rotating speed of the engine due to variation in engine torque accompanied by cyclic ignitions (explosions) in an engine cylinder and reciprocating motion of a piston. This results in a forcing source (such as a vibrating source and vibration forcing power). Vibrations are transferred to a vehicle vibrating system such as an engine suspension system, structured with a power plant in which the engine and the transmission (or the transaxle) are coupled to each other, an exhaust system and a vehicle body system or the like. This vibration is amplified due to a resonating phenomenon of the vibrating system of the vehicle, which results in the occurrence of vibrations and confined sounds in various parts of the vehicle.
It has heretofore been well known that such a resonating phenomenon occurs in a given engine speed range that acts as a resonating region. The engine speed lies at, for instance, the given engine speed range less than an idling speed, and a probability exists for the resonating region to occur when the engine speed transits the given engine speed range on a stage in which the engine speed is raised during the start-up of the engine.
With the hybrid vehicle disclosed in JP 2003-127679A, the rotating speed of the first electric motor is increased during the start-up of the engine. It is conceived that if the engine speed is caused to rapidly increase to a level higher than the given engine speed, the engine speed can rapidly transit the resonating region in the engine speed range less than the idling speed whereby vibration and noise are suppressed during the start-up of the engine.
Thus, with such a drive apparatus for vehicle enabled to address the issue of the drive apparatus for the hybrid vehicle, it is desired to similarly suppress the vehicle from encountering the occurrence of vibration and noise during the start-up of the engine.
In an alternative, further, during the halt i.e., stop of the engine, a probability exists where during a halt of the engine, the engine speed falls in the given engine speed range on a stage where the engine speed is caused to decrease to a zero, that is, a rotational halt of the engine. Therefore, with the drive apparatus for vehicle enabled to address the issue of the drive apparatus for the hybrid vehicle, it is desired for the drive apparatus for vehicle to similarly suppress the occurrence of vibration and noise during the halt of the engine.
The present invention has been completed on the background with the above problem in mind and has an object to provide a control apparatus for a drive apparatus of vehicle, including a differential mechanism, operative to perform a differential action to distribute an engine output to a first electric motor and an output shaft, and an electric motor provided in a power transmitting path from the differential mechanism to drive wheels, which can minimize the drive apparatus in size or improves fuel economy while suppressing the occurrence of vibration and/or noise of a vehicle during a start-up or a halt of the engine.